The challenge of determining the role of Rh glycoproteins in transport of NH_3 and NH4+

摘要

The mammalian Rh glycoproteins belong to the solute transporter family SLC42 and include the erythroid Rh-associated glycoprotein (RhAG) and two epithelial membrane molecules Rhbg (human RhBG) and Rhcg (RhCG). Mammalian Rh glycoproteins are closely related to the ammonium transporters of the yeast (MEP proteins) and bacteria (Amt). Rhbg and Rhcg are expressed in several mammalian tissues including liver, kidney, skin, lung, and GI tract. In the kidney they are expressed in a-intercalated cells and principal cells of the collecting duct. Whereas Rhbg is strictly present in the basolateral membrane; Rhcg is reported to be at both apical membrane and basolateral membranes. Recent functional studies strongly support a role of Rh glycoproteins in NH4+ transport. Other studies indicate that they mediate transport of CO_2 and NH3. This review highlights the progress in determining the properties of Rh glycoproteins and the challenging questions that continue to hinder understanding their function and their physiological role.